1. Field of the Invention
The present invention relates to a decoder and a receiver employed in a satellite broadcasting system, a satellite communication system, a terrestrial broadcasting system, a terrestrial communication system, or the like.
2. Related Art
A receiver in a satellite broadcasting system, a satellite communication system, a terrestrial broadcasting system, or a terrestrial communication system using code division multiplex access (CDMA) down-converts a signal of a radio frequency (RF) received from a transmitting station, and subjects the down-converted received signal to a code division multiplex (CDM) demodulation. The receiver calculates soft decision data (multivalued input level) to be input to a Viterbi decoder based on a CDM-demodulated signal. More specifically, the receiver calculates the soft decision data by applying the demodulated signal for a soft decision table (soft decision information) in which intervals obtained by dividing between a highest level and a lowest level according to a plurality of thresholds corresponds to pieces of soft decision data. The Viterbi decoder in the receiver performs a Viterbi decoding based on a Viterbi algorithm using the calculated soft decision data.
The conventional receiver has, however, the following disadvantages. Since each threshold interval is fixed in the soft decision table, an optimum coding gain is not always obtained on a low-quality line (e.g., in case of great influence by fading or in case of many multipaths).